Actually post natal/ post partum depression can last for years, and in some cases can even be delayed for years.
I would say possibly that counselling sometimes makes some people in your scenario feel worse. Does your wife feel angry and judged about it? If so then I'd personally advise you to try and get childcare for the day and take the whole day with your partner to show her exactly how much you love her (in a non sexual way) and try to get her to open up one to one with you and tell you exactly how she feels. You must ask her for complete honesty and expect things you may not wish to hear without being in any way judgemental. She clearly needs your support and love, she's just having a very hard time at the moment allowing herself that luxury.Communication is the only way forward, so you have to at some point talk honestly together.